Static mixer

ABSTRACT

The static mixer has a static rigid mixing unit contained in a coaxial barrel which is mounted at its ends, respectively, in an inlet header through which materials to be mixed are fed under pressure to and through the unit, by which they are mixed, and in an outlet header through which the mixture is discharged. The unit comprises a row of vanes arranged to divide the material into separate streams, reassemble them in different combinations, and redivide and combine the combinations, repeatedly, as the material passes through the unit. The characteristic feature is that the barrel and unit are composed of different materials so related that the barrel can be destroyed readily, or rendered readily destructible, by means which, when and as applied to the combined barrel and unit so that both are subjected thereto, leaves the unit substantially intact.

Unite States Patent Potter [451 Jan 18, 11972 [54] STATIC MIXER PrimaryExaminerRobert W. Jenkins Attorney-John Harrow Leonard [72] Inventor:Charles Potter, Lakewood, Ohio [73] Assignee: AMVIT, Cleveland, Ohio[57] ABSTRACT [22] Filed: Sept 8, 1970 The static mixer has a staticrigid mixing unit contained in a Appl. No.: 70,288

coaxial barrel which is mounted at its ends, respectively, in an inletheader through which materials to be mixed are fed under pressure to andthrough the unit, by which they are mixed, and in an outlet headerthrough which the mixture is discharged. The unit comprises a row ofvanes arranged to divide the material into separate streams, reassemblethem in different combinations, and redivide and combine thecombinations, repeatedly, as the material passes through the unit.

8 Claims, 3 Drawing Figures STATIC MIXER This invention relates to astatic mixer and particularly to a static mixer of the general typedisclosed in US. Pat. No. 3,286,992 of Nov. 22, 1966.

Such static mixers have been found very effective for mixing moldableplastic compositions, usually by the introduction thereinto of solubleplastic material, filler, solvent, and catalytic setting agent.Generally such a mixer can be used for a few hours after which it mustbe flushed out with a suitable solvent, but after a period of about aweek or two it must be replaced with an entirely new and clean mixer.

When used, however, for mixing quick-setting plastic compositions, anadditional problem is involved. Due to thequicksetting characteristics,the flow throughthemixer must be at a rate above a predeterminedminimum, or else the plastic will set up within the mixer instead ofbeing discharged into the usual succession of molds which generallyaremoved on suita ble belts past the discharge of the mixer in timedrelation to the discharge therefrom. If for any reason a slight delay ordecrease in rate of the passage of the plastic mixture through the mixeroccurs, the mixture sets up in portions of the mixer and restricts theflow, thus further slowing the discharge and resulting in the entiremixer being clogged with the hardsetting plastic. Generally such staticmixers are in the form of a tubular barrel in whichis arranged a rigidstatic mixing unit. The mixing unit generally comprises fixed mixingvanes arranged in a row which extends endwise of the barrel. The vanesare arranged so that as the material is discharged from one vane itdischarges with a swirling action about the axis of the barrel andstrikes the next vane which subdivides the stream before passing it onto the next succeeding vane which subdivides these subdivisions. At eachsubdivision, each subdivided stream is recombined with a subdividedstream different from the one from which it was subdivided the instantbefore. Thus as the materials pass through the length of the barrel, thestream is subdivided and recombined in many different subcombinations somany times that a completely homogeneous mixture is discharged from thedischarge end of the mixer. By the very nature of these vanes, however,and their arrangement in the barrel, they cannot be cleaned readily onceany appreciable quantity of plastic has set up in the variousinterstices and along the serpentine passages defined by the unit andthe barrel.

Attempts have been made to make the barrel, headers, and unit readilyseparable for cleaning, but due to the cementing and interlockingeffects of the plastic, this approach has proven impractical.

Also attempts have been made to clean by introducing plastic solvents,but they cannot be circulated effectively through the tortuous passagesin the units, especially when the entire flow has been blocked at somelocation in the mixer.

Heretofore the vanes of these units have been made of very durablematerial, such as a stainless steel, carbon steel, glass, titanium, orTeflon, and the barrel made of ordinary steel. While this type ofstructure can be cleaned, provided only a very small amount of settableplastic accumulates therein and is of a type that can be dissolvedreadily, it cannot be cleaned once a substantial amount of plastic hasformed in any one place or the mixer has become completely clogged. Thisis due primarily to the inaccessibility of the plastic, by solvents, inportions of the passages through the barrel and vane unit, orinaccessibility inherent if the vanes are arranged for efi'rcientmixing. For like reasons, an effective air supply cannot be applied tothe clogging plastic in the mixer for use in burning out the plasticeffectively.

In accordance with the present invention, however, the outer case orbarrel is made of a material which is so related to the material ofwhich the vanes are composed that, the barrel can readily be destroyedor rendered readily destructible by means which when applied in theintended manner to the combined barrel and unit for the destruction ofthe barrel leave the vane units and headers substantially intact.

The specific material of the barrel per se and of vane unit per se issecondary. It is the relation of the material of the one to the materialof the other that is controlling. If the barrel is removed by destroyingit by means which do not affect the headers and unit when applied to theentire assembly, then all parts of the vane unit are rendered readilyaccessible for cleaning by the application of chemicals, heat,mechanical forces, or other means.

For example, the barrelmay be formed of plastic, ceramic, or othermaterial which can be readily fragmented, burnt or melted off, slit andpulled off, shattered at room temperature or in frozen condition, ordissolved chemically by means which, when and as applied to the mixer,does not deleteriously affect the material of the vane unit. The vanes,therefore, must be of a material such that they willnot be deleteriouslyaffected or changed substantially in any manner as the result of themeans used for destroying the barrel. Assuming that the vanes are of ahard metal, suchas steel or the like, the barrel may be made of aplastic which can be burnt off or rendered very frangible readily attemperatures around 400 F. which, of course, would not affect the steelappreciably. Generally the 'quick settingplastic is of a compositionwhich can be burnt off the vanes at this same temperature, once adequateair can gain access to it. lnthe method of cleaning by heat, the entiremixer is placed. in an oven and heated to the temperature requisite toburn up and consume the barrel or to render it very frangible so that itcan be fragmented and broken off readily,'thereby exposing the vane unitand all the intricate passages within the vane unit for cleaning.Generally all that is necessary is to heat the entire combination ofcasing and unit and then with a heavy brush, brush off the weakenedplastic barrel and the plastic adhering to the vanes themselves.

Polyvinylchloride, polyethelene, and other types of commerciallyavailable synthetic plastic pipes have been found to be effective forthe barrels, so long as the unit is of a material which would not bedestroyed by the destruction of the barrel.

On the other hand, the outer barrel may be of a metal which can bedissolved chemically by a solvent which would not adversely afiect thevane unit, in which case the vane units are readily exposed for cleaningby any conventional means.

Again, the barrel might by of ceramic or glass or a composition whichcan readily be fragmented by a series of sharp blows without damage tothe vane unit or headers.

Thus by using for the barrel a material properly related to the materialof the vane unit, the cleaning problem is simplified so that cleaningcan be effected at very little expense in man-hours, materials, and downtime. Such cleaning can be effected by an average workman in the plantwhere the unit is in use.

A preferred embodiment of the invention is illustrated in the drawings,in which:

FIG. 1 is a side elevation of a mixer embodying the principles of thepresent invention;

FlG. 2 is a cross-sectional view of the mixer taken on line 2-2 ofFlG.1; and

HG. 3 is a cross-sectional view of the mixer taken on line 3-3 of FIG.1.

In the illustrative example, the mixer, indicated generally at l,comprises a tubular barrel 2 having at its inlet end a feed header 3 andat its outlet end a discharge header 4. The feed header is provided withone or more feedpipes or ducts 5 which supply the separate ingredients,or a preliminary mixture thereof, as preselected, into the header underpressure sufficient to cause a relatively rapid flow of the materialthrough the mixer.

Within and coaxial with the barrel 2 is a static vane mixing unit 6which is in the form of a plurality of blades 7 which may be directlyfastened together or fastened to a center rod or support. The blades arearranged in a row extending from one end of the barrel to the other and,if desired, the row may be connected at its ends to the headers. Theouter periphery of the vanes of this mixing unit may fit rather snuglyagainst the interior wall of the barrel 2, but may terminate closethereto and not necessarily bein sealing relation thereto.

The vanes 7 are arranged so that the material entering through theheader 3 is divided initially at that end of the barrel and unit. Thetwo streams resulting from this division pass to the next vanes whichsubdivide each of these streams and recombines each subdivided streamwith another subdivided stream different from the one from which it waspreviously subdivided. As the material passes to successive vanes,further subdividing and combining are caused so that by the time thematerial reaches the discharge header 4, a multitudinous number ofstreams have been divided, subdivided, and intermixed with each other toan extent such that the mixture discharged from the mixer issubstantially homogeneous and uniform throughout.

The discharge header 4 is provided with a discharge pipe 8 which isarranged to discharge into molds, not shown, which are movedsuccessively therebeneath. The timing for as short a cycle as possibleis important from the economic standpoint and hence it is desirable topass the material through the mixer at the maximum rate permissible,this rate, of course, depending on the nature of the plastic materialwhich is passed through the mixer and the viscosities and chemicalcharacteristics. The materials are supplied to the mixer under pressureso as to maintain the proper flow, but in seeking as short a cycle aspossible, the danger of setting up" of the material because of a slightincrease in resistance to flow slowing down the stream is increased.

The specific type of vane unit, of course, is dictated to some extent bythe type of materials which are to be mixed. This dictates, in turn, thetype of material to be used for the barrel and the type of destructionof the barrel casing to be employed to afford access to the vane unitfor cleaning.

It is apparent from the foregoing description that regardless of howbadly clogged the unit may become, cleaning is made possible by therelative destructibility and indestructibility of the barrel and vaneunit, respectively.

The invention is also applicable to mixers with other types of mixingunits operating in a barrel or container where clogging by setting up"or by sludge due to increase in viscosity, and the like, occur and theinterior is inaccessible for cleaning in the assembled relation of theparts.

Having thus described my invention, 1 claim:

1. A continuous static type continuous mixer for flowable ingredients ofa quick-setting plastic fed continuously under pressure and for mixingthe ingredients and discharging the resultant plastic in flowablemoldable condition, comprising:

a tubular barrel;

a header on one end of the barrel adapted for connection to a source forreceiving the ingredients under pressure and admitting the receivedingredients into the barrel;

discharge means at the other end of the barrel;

a static rigid mixing unit within the barrel and comprising a row ofmixing vanes extending endwise of the barrel and arranged so that thestream of material is caused to flow through tortuous paths and to besubdivided and the subdivided streams mixed repeatedly as the materialpasses through the barrel to the discharge means;

said barrel being composed of a material different from that of thevanes, said material being such, relative to the material of the vanes,that saidmaterial can be destroyed or rendered readily destructible bymeans which, when and as applied so that the combined barrel and unitare subjected thereto, leave the vanes substantially intact.

2. The structure according to claim 1 wherein the barrel is composed ofmaterial which is rendered readily destructible by the application ofheat to the combined barrel and unit at predetermined low temperaturesbelow temperatures which have deleterious effects on the unit.

3. The structure according to claim 1 wherein the barrel is composed ofmaterial which is soluble readily in a solvent in which the unit isinsoluble.

4. The structure according to claim 1 wherein the barrel is composed ofmaterial which can be broken into fragments readily by mechanical forceswhich, as applied to the combined barrel and unit, leave the vanessubstantially intact.

5. The structure according to claim 1 wherein the barrel is set plasticmaterial.

6. The structure according to claim 5 wherein the barrel is ceramicmaterial.

7. The structure according to claim 5 wherein the unit is of hard metal.

8. The structure according to claim 1 wherein the barrel is composed ofsynthetic organic plastic and filler and the vanes are ferrous metal.

1. A continuous static type continuous mixer for flowable ingredients ofa quick-setting plastic fed continuously under pressure and for mixingthe ingredients and discharging the resultant plastic in flowablemoldable condition, comprising: a tubular barrel; a header on one end ofthe barrel adapted for connection to a source for receiving theingredients under pressure and admitting the received ingredients intothe barrel; discharge means at the other end of the barrel; a staticrigid mixing unit within the barrel and comprising a row of mixing vanesextending endwise of the barrel and arranged so that the stream ofmaterial is caused to flow through tortuous paths and to be subdividedand the subdivided streams mixed repeatedly as the material passesthrough the barrel to the discharge means; said barrel being composed ofa material different from that of the vanes, said material being such,relative to the material of the vanes, that said material can bedestroyed or rendered readily destructible by means which, when and asapplied so that the combined barrel and unit are subjected thereto,leave the vanes substantially intact.
 2. The structure according toclaim 1 wherein the barrel is composed of material which is renderedreadily destructible by the application of heat to the combined barreland unit at predetermined low temperatures below temperatures which havedeleterious effects on the unit.
 3. The structure according to claim 1wherein the barrel is composed of material which is soluble readily in asolvent in which the unit is insoluble.
 4. The structure according toclaim 1 wherein the barrel is composed of material which can be brokeninto fragments readily by mechanical forces which, as applied to thecombined barrel and unit, leave the vanes substantially intact.
 5. Thestructure according to claim 1 wherein the barrel is set plasticmaterial.
 6. The structure according to claim 5 wherein the barrel isceramic material.
 7. The structure according to claim 5 wherein the unitis of hard metal.
 8. The structure according to claim 1 wherein thebarrel is composed of synthetic organic plastic and filler and the vanesare ferrous metal.